1. Field of the Invention
The present invention relates generally to photographic cartridges, and more particularly to a pulse generating mechanism for a web-roll mounted for rotation within a cartridge.
2. Description of the Prior Art
Sensing mechanisms for sensing web rotation, or web transport, are well known in the prior art, as indicated in U.S. Pat. Nos. 3,564,219, 3,730,453, 3,779,483, 3,917,142, 3,949,856, and 4,153,361.
Most of those patents utilize some type of sensing mechanism wherein pulses are generated for indicating a rotational velocity of the web-spool. The pulses are fed to a counter, where they are accumulated, stored, and displayed to indicate the amount of web material remaining on the spool.
One problem with prior-art sensing mechanisms, including pulse generating portions thereof, is that, mechanically, they are of relatively complicated construction, which adversely affects the reliability and cost of such mechanisms. One disadvantage of those mechanisms is that the web-roll cartridge normally interfaces with a printer or the like, and the sensing and pulse generating mechanisms are normally mounted in the interfacing structure and not within the cartridge. That necessitates a larger and more complicated interfacing structure. Another disadvantage of prior-art sensing and pulse generating mechanisms is that most of them are designed to deal with cartridges that handle web material which is insensitive to light. Such mechanisms, particularly the pulse generating portion thereof, could not be incorporated into apparatus having cartridges containing photosensitive web material without exposing the web material and thus making the apparatus inoperative. Prior-art sensing mechanisms that are capable of handling photosensitive web material and generating pulses for some specified purpose without exposing the web material, such as those mechanisms disclosed in the above-cited U.S. Pat. No. 4,153,361, are wholly located outside the cartridge, thereby suffering from the disadvantage first mentioned above. The pulse generating mechanism of this invention is believed to eliminate those and other disadvantages of the known prior art.